1. Field of the Invention
This invention relates to materials usually called particleboards, fiber boards, flakeboards, hardboards, strand boards, slats for pencil stock, and the like, produced by consolidation of furnishes consiting of lignocellulosic fibers and particles with or without adhesive coatings, impregnating materials, water repellents, preservatives, fire retardants, fillers, or other additives. The fibers and particles may be derived from natural products such as wood, bark, straw, grass, bagasse, and the like, or any combination of these or similar materials, or from other natural or synthetic organic or inorganic materials. Said particles may be in the form of flakes, strands, fibers, fiber bundles, shavings or combinations of these. The only limitation on particle form or shape for the effective operation of the method of this invention is that a substantial portion of the particles should be elongated in the stronger, or grain direction of the material from which the particles are formed. Methods of formation of such particles are well known in the previous art.
2. Description of the Prior Art
The present invention differs from the following two categories of prior art: The first category is that of mechanical orientation involving free-fall of elongate particles through parallel arrays of stationary or vibrated baffles, bars, or slots. Such mechanical methods, however, are only amenable to orientation of relatively large strands, splinters, or long flakes, one of the reasons being that achievement of good orientation by such means depends on maintaining the distance from the bottom of the confining baffles, bars, or slots to the top of the forming mat below, to be just a little less than the length of the particles to be oriented. This requirement renders such methods impractical for wood fibers or particles of small dimension because the free surface of the forming mat cannot be relied upon to be planar, but is subject to irregularities of greater magnitude than the length of wood fibers and other small particles. Another related disadvantage of the mechanical methods of orientation is that if the apparatus is designed and adjusted for one length of particle, it will afford little or no orientation for shorter particles, and it is difficult to prepare a particleboard furnish without inclusion of a considerable amount of such shorter particles unless considerable waste is acceptable.
The second category of prior art is that involving electrical field means of causing a single layer of particles such as abrasive grits or carpet pile to be aligned perpendicularly to an adhesive-coated substrate to which they are to be attached. Such methods and apparatus involve placing a net charge on substrate and particles and would be totally inapplicable to the object of the present invention which requires building up a thick mat of particles directionally aligned in the plane of the mat.